Theophylline is a drug currently used by most asthmatic/allergic adults and children, constituting over six million patients. Therapy requires frequent monitoring of theophylline levels in blood as it causes toxicity at concentrations higher than 20 mg/L and is ineffective at lower than 10 mg/L. Current testing is done in hospital/commercial laboratories at a cost of $27.00 per test to Medicare/Medicaid. There is great need for a cost effective, easy to perform test for theophylline so that physicians, in their offices, or patients can quickly monitor this drug by using a drop of whole blood from a finger tip. Current tests for theophylline use antigen-antibody technology and are cumbersome and expensive. Alternatively, GDS Technology's discovery of a new enzyme, namely Theophylline Oxidase, which selectively oxidizes theophylline could enable the development of a simple, convenient, and specific enzymatic test. This proposal (Phase I) focuses on initial feasibility studies and will include studying the properties of this enzyme to establish its suitability for a commercial test. The goal of Phase II will be the development of a convenient enzymatic dry chemistry test for theophylline which will cost $1.00-2.00 and thus will greatly reduce health care cost.